The present invention relates to room temperature vulcanizable silicone rubber compositions (room temperature vulcanizable will hereafter be referred to as RTV) and more particularly the present invention relates to RTV silicone rubber compositions which are alkoxy functional, shelf stable, and fast curing.
One component RTV silicone rubber compositions are well known. Basically, the earliest of such compositions comprised mixing in a substantially anhydrous state, a silanol end-stopped diorganopolysiloxane polymer, with or without filler, with an acyloxy functional cross-linking agent in the presence of a condensation catalyst. This composition by itself or with other ingredients was stable and a fluid in the substantial absence of moisture. But when exposed to atmospheric moisture would cross-link to form a silicone elastomer; see for instance Ceyzeriat, U.S. Pat. No. 3,133,891 and Bruner U.S. Pat. No. 3,035,016.
As development progressed in this area, compositions were produced in which the cross-linking agent had functionality other than acyloxy functionality such as amine functionality, amide functionality, alkoxy functionality, etc. One particular useful functionality for such one component RTV silicone rubber composition was alkoxy functionality. An example of an RTV composition which has such alkoxy functionality is for instance to be found in Beers U.S. Pat. No. 4,100,129. There are a great number of patents in this area and all of them cannot be gone into. Suffice it to state that there were many variations and particularly patented variations of a one-component RTV silicone rubber composition in which the cross-linking agent was an alkoxy functional silane and in which the curing catalyst was a chelate and preferably a titanium chelate of which the foregoing Beers U.S. Pat. No. 4,100,129 is exemplary.
One of the advantages of such compositions was basically that it was non-corrosive; that is, upon hydrolysis of the cross-linking agent and curing of the composition, it emitted an alcohol which is substantially non-corrosive to most substances. Further, the composition did not emit a pungent odor and the cured silicone rubber composition had all the properties of silicone elastomers. However, such compositions had some disadvantages in that they were not as fast curing as would be desired; and, in some cases, after storage periods of six months or a year or more would not cure or would cure very slowly. As a matter of fact, some subsequent detailed studies of such compositions after the foregoing patents were obtained and after the compositions had been commercialized, indicated that the cure rate of shelf stability of the compositions was affected after storage periods as small as two weeks or a month.
There were many hypothesis put forward as to why the slowing of the cure rate occurred. One hypothesis for instance was to be found in the patent application of White, et al, Ser. No. 277,524, filed June 26, 1981, now U.S. Pat. No. 4,395,526, which postulates that excess hydroxy groups in the compositions hydrolyzed the alkoxy groups on the end capped polymer making the polyalkoxy functional polymer resistant to curing or slowing down the cure rate. The inventors of the White, et al, patent application attempted to solve this difficulty by the use of scavenger compounds and integrated cross-linker, scavenger compounds which would because of the scavenging groups react and tie up hydroxy groups in the polymer system, thus resulting in most of the polymer composition having polymers in which the alkoxy functional groups remain intact. It was postulated and as the experimental results indicate, the result was a shelf stable, one component RTV alkoxy functional composition. Also see the patent application of Halgren, Ser. No. 277,525, filed on June 26, 1981, now U.S. Pat. No. 4,377,706, which relates to a process for producing certain scavengers which are utilized in the White, et al, systems.
Other patent applications in this area which deal with the use of integrated cross-linker scavengers to tie up free hydroxy groups in the RTV polymer composition so as to result in a shelf stable, fast curing one component RTV system are as follows: Chung, Ser. No. 338,518, filed Jan. 11, 1982, now U.S. Pat. No. 4,424,157; Beers, Ser. No. 349,537, filed Feb. 17, 1982, now abandoned; Dziark, Ser. No. 349,695, filed Feb. 17, 1982, now U.S. Pat. No. 4,417,042; and Lucas and Dziark, Ser. No. 349,538, filed Feb. 17, 1982, now U.S. Pat. No. 4,483,973. Of particular interest is the patent application of Dziark, which deals with the use of silazanes as solely scavenging agents which are introduced into the RTV system after the silanol containing diorganopolysiloxane polymer is end capped with the alkoxy functional cross-linking agent which most frequently is methyltrimethoxysilane.
In the other patent applications, there is disclosed that there may be utilized optionally an alkoxy functional silane as an integrated cross-linking scavenger agent which has the properties specified. It is disclosed in those patent applications, that to end cap the silanol, end-stopped polysiloxane polymer with a polyalkoxy functional silane, it is necessary to use an end capping catalyst which is disclosed to be preferably an amine such as di-n-hexylamine. It should be noted that while polyalkoxy silanes will condense or react with a silanol end-stopped polysiloxane polymer to end cap it, this reaction takes place very slowly or not at all without an end capping catalyst. This is even true where there is utilized one of the integrated cross-linkers scavengers of the foregoing White, et al, patent application, Ser. No. 277,524, U.S. Pat. No. 4,395,526, as well as those of the other patent applications above. However, even such basic end capping catalysts of the White, et al case are not as effective as would be desired. This is particularly true for instance in the one component alkoxy functional RTV system of Chung, et al, Ser. No. 428,038, entitled, Novel Scavengers for One-Component RTV Compositions, filed on the same date as the present case.
In Chung, et al, Ser. No. 428,038, there is disclosed a utilization of an alkoxy functional silazane integrated cross-linking agent scavenger. Such an integrated cross-linking agent, scavenger desirably needs a fast end-capping catalyst so that the integrated cross-linker scavenger may react with the silanol end-stopping diorganopolysiloxane polymer to end stop it to produce a shelf stable RTV polymer system. It has been found that the basic amine end capping catalysts are not very effective in such systems.
Accordingly, it is one object to provide for a shelf stable, fast curing, non-corrosive, alkoxy functional, one component RTV system.
It is another object of the present invention to provide for an efficient and rapid end-capping catalyst for reacting polyalkoxy silane and siloxane cross-linking agents with silanol containing polysiloxane polymers so as to end-cap the polymer with the polyalkoxy silane in an efficient manner.
It is an additional object of the present invention to provide a very efficient and rapid end-capping catalyst for integrated cross-linkers, scavengers which are reacted with silanol containing diorganopolysiloxane polymers to produce shelf stable, one component RTV systems.
It is yet still an additional object of the present invention to provide a process for producing a shelf stable, one component, alkoxy functional, RTV system by use of efficient end-capping catalysts for the reaction of polyalkoxy silane and siloxane cross-linking agents with silanol-containing organopolysiloxane polymers.
It is further still an additional object of the present invention to provide a process for producing a shelf stable, rapid curing, one component RTV system by providing an efficient end-capping catalyst for the reaction or end-capping of a silanol-containing organopolysiloxane polymer with an integrated cross-linker agent scavenger.
These and other objects of the present invention are accomplished by means of the disclosure set forth herein below.